Planetary gear trains have the advantage over pinion type gearing by permitting higher power densities, large gear ratios, and concentric power input and output. Increased power requirements in planetary gear trains are usually accommodated by increasing the diameter and width of the gears. If there are restrictions on the diametrical size of the gear train, increases in power can be met only by increasing the width of the gears or upping the material and machining specifications. There are practical limits to both these approaches.
An apparent solution for increasing power capacity within a limited diametric size is to add more gear sets to the train so that power is shared between more than one gear set. This results in a lesser load for each gear set but a higher total power capacity. However, there are severe practical problems with such a solution. This solution requires nearly perfect power sharing among the several gear sets. Such perfect power sharing among the gear sets would require manufacturing tolerances for the gears which are not practical for the vast majority of commercial applications. Practical manufacturing tolerances for the gears would result in uneven power sharing. Such uneven power sharing or uneven loading results in one set of gears being loaded more heavily than its designed for. This results in excessive wear and/or premature failure.
Gear transmissions having pairs of helical gears mounted on a drive shaft for engagement with respective pairs of helical gears mounted on a driven shaft are disclosed in copending U.S. patent application Ser. No. 09/167,760 filed Oct. 7, 1998 entitled Improvements In Power Sharing Gear Sets. The disclosures, including the disclosures of the specification and drawings, of prior U.S. patent application Ser. No. 09/167,760 filed Oct. 7, 1998 are hereby expressly incorporated by reference into this present application. The use of paired helical gears in multi-speed automotive transmissions is disclosed in U.S. patent application Ser. No. 09/187,905 filed Nov. 6, 1998 entitled Multi-Speed Automotive Transmission Using Paired Helical Gearing. The disclosures, including the disclosures of the specification and drawings, of prior U.S. patent application Ser. No. 09/187,905 filed Nov. 6, 1998 are hereby expressly incorporated by reference into this present application.